Revert change to how expiration timings to calculated.

[gurudesu]

When testing upgrading from v3.0.2 to v3.1.0, I've noticed a small bug impactful (to me) change around how expirations are calculated.

If you set a LifeWindow of 1s, add an entry, and wait 1100ms, the entry does not expire. Testing it a bit more, I've discovered that it actually expires if you wait 2s.

You can see this regression in code when comparing the old logic here with the new logic here.

For convenience, old logic:

if currentTime-oldestTimeStamp >= s.lifeWindow {
}

new logic:

return currentTimestamp-oldestTimestamp > s.lifeWindow

This change reverts that logic to the old behavior.

[gurudesu]

This test case conflicts with the test name - if the name is Expired maybe it should be expected to be expired.

This patch has that desired behavior.